C57BL/6 mice develop alopecia and dermatitis which can progress to ulcerative dermatitis, and premature morbidity and mortality. Female mice are more susceptible than male mice. The etiology is unknown, however, it was reported that the incidence of skin lesions decreased from 5.5% to < 1.0% when C57Bl/6J mice were switched to the NIH-31M diet. Studies were initiated to determine whether specific dietary ingredients would reduce the severity of dermal lesions and extend the survival rates in female C57BL/6N mice as they age. After eleven months, no significant differences were observed in survival rates between mice receiving test or control diets. At 26 months of age, survival rates for mice receiving the cyanocobalamin (B12) fortified diet were significantly higher (p<0.01) than mice fed the control diet. Mice receiving the test diets fortified with choline, biotin, pyridoxine (B6), animal tallow, vitamins D or E had increased survival rates and/or thicker, sleeker hair coats than mice receiving the control diet. Conclusion: that 1) cyanocobalamin (B12), choline, vitamin D and animal tallow may play a more important role than previously thought in reducing skin lesions and extending the survival rates of C57BL/6N mice, and 2) C57BL/6 mice may require dietary changes as they age to compensate for natural degenerative skin changes that occur, probably due to strain dependent genetic predispositions. - alopecia, animal feed, animal nutrition, mice, inbred strains, dermatitis